The syntheses of organosilanes and organosilicone polymers are well known and generally involve catalytic hydrosilylation of an aliphatically unsaturated compound with a silane or a silicon polymer containing reactive silanic-hydrogen, ##STR1## and/or hydrogen-siloxy, ##STR2## units in the presence of small amounts of acidic platinum catalyst, e.g. chloroplatinic acid. While relatively high conversions to organosilanes and organosiloxanes are achieved, the crude product is unsuitable for many applications since it has a hazy appearance or amber coloration which is caused by entrainment of extremely low levels (ppm), of residual platinum catalyst. Such products are particularly unsuitable for cosmetic and personnel use applications. More importantly, because of the high cost of platinum catalysts, it is economically judicious to recover even small residual amounts from the crude product mixture and preferably to recover the platinum in a purity suitable for reuse. In prior operations, where product is recovered by neutralization and filtration, these small amounts of platinum are generally unrecoverable from the filter cake.
One method which has been proposed for removal of platinum involves the neutralization of the reaction product with an excess of metal bicarbonate and the use of pressure filters to remove the resulting salt. Although this method accomplishes some lightening of the highly colored product, it is inefficient and fails to provide a truly clear, colorless product.
Several other methods have been proposed for removal of platinum catalyst to reduce haze and coloration of the organosilane/organosilicone product. Such methods include the treatments involving tedious and time consuming extractions with liquids, filtrations or contact of the reaction mixture with clays, magnesium silicate or magnesium sulfate decolorization agents or filtering aids. However, the high concentration of inorganic clarifying agents needed to achieve a reasonably clear product, prevent recovery of platinum by economical methods. Accordingly, these traces of platinum catalyst entrained in the inorganic clarifier are lost in the process.
Still another method, such as that disclosed in U.S. Pat. No. 3,745,206, involves contacting the reaction mixture from which platinum catalyst is to be removed with a solid carrier having a thiol or thioether functional silicone bonded to its surface and subsequent washing with aqua regia to dissolve and separate entrained platinum from the solid carrier. Since the removal of platinum catalyst from the reaction mixture depends on entrainment in the solid carrier, relatively large amounts of this silicone surface carrier must be used and consequently significant amounts of aqua regia are required to recover the platinum from the carrier. Also, the recovery of platinum by this method requires special corrosion resistant equipment and involves handling and disposal of hazardous corrosive concentrated acids which renders the entire process environmentally objectionable and economically unfeasible for commercial use.
Accordingly, it is an object of this invention to overcome the disadvantages described above and to provide a clear, substantially colorless organosilane or organosiloxane product.
Another object of this invention is to provide a simplified, more efficient process which employs inexpensive chemicals of low toxicity.
Another object of this invention is to provide a process for the recovery of trace amounts of a platinum group metal catalyst form an organosilane or organosiloxane synthesis mixture and from the organosilicone products or from other synthesis mixtures and products.
Another object is to recover the platinum group metal catalyst in the form of elemental metal and in a high yield and purity suitable for reuse in catalytic or other reactions.
Another object is to recover platinum in the form of a platinum salt or as chloroplatinic acid in high yield and purity.
Still another object of the invention is to provide simultaneous neutralization of a hydrosilylation reaction mixture while removing color and haze from the organosilane and organosiloxane product.
Another object is to accomplish all of the above objectives by a commercially feasible and economical process.
These and other objects of the invention will become apparent from the following description and disclosure.